1. Field of the Invention
The invention relates to bimetallic catalytic systems and their applications, and in particular to selectively hydrogenate olefinic unsaturation in diene polymers and copolymers, comprising nitrile rubber (acrylonitrile-butadiene rubber; NBR)
2. Description of the Related Art
Selective hydrogenation of unsaturated carbon-carbon double bonds of nitrile rubber results in a product that is resistant to oils, ozone and sour gases, while maintaining a high service temperature. As a result, such compositions find particular utility in automotive applications like oil seals, timing belts and hoses, in which formed rubber products are exposed to adverse environments and sustained high temperatures. Thus, it is desirable to produce a hydrogenated nitrile rubber (HNBR) composition having the advantageous mechanical and resistance properties described above.
Hydrogenation of NBR is usually effected by hydrogen in an organic solvent, using homogeneous precious metal catalysts to achieve quantitative carbon-carbon double bond reduction, without concurrent hydrogenation of non-olefin functionality such as nitrile groups. Organometallic compounds comprising rhodium (Rh) as a catalyst are disclosed in GB 2,070,023, U.S. Pat. No. 4,465,515 and U.S. Pat. No. 4,503,196 etc. Rhodium catalyst provides high hydrogenation efficiency and selectivity, while their drawback is high cost.
Ruthenium (Ru) complexes as hydrogenation catalysts is disclosed to reduce cost in U.S. Pat. Nos. 4,631,315; 4,673,757; 4,747,707; 4,795,788; EP 0,405,266A2 etc. The advantage of Ru complex catalyst is its high catalytic activity in hydrogenation, with the drawback of comparatively low selectivity due to side reactions and gel formation.
Therefore, there is a need for a catalyst system which has higher activity, lower cost and results in no severe side-reactions in the hydrogenation reaction. Thus, there is still a need in searching for highly efficient and relatively low-cost methods of fabricating HNBR.